Andrew Lau Wai-keung said he and his crew spent more than a year researching Chinese history before making The Founding of an Army and that the use of young actors in key roles reflected the situation when the People’s Liberation Army was formed in the 1920s.

“I see no reason for using 40-year-old actors to play the roles of people who were just in their 20s in the movie,” Lau said. “I am very familiar with the history now. In fact, I have become an expert.

“I am particularly familiar with what happened between 1919 and 1946. I did not study well when I was a kid but I studied for this movie.”

Lau made the remarks as the film premiered in Hong Kong on Sunday, three days after its release in mainland China.

It set off a storm after Ye Daying, grandson of the late communist general Ye Ting, wrote an open letter of protest with other descendents of renowned military figures, such as generals Zhu De and Ye Jianying, to the State Administration of Press, Publication, Radio, Film and Television.

The letter, posted on Ye’s weibo account, mainland China’s answer to Twitter, said: “It is surprising and worrying to see the producers hired an entertainment movie director who is no expert on revolutionary history.”

It added that the production team had put box office takings ahead of historical facts, then went on to say: “It is a good thing to see excellent young actors playing revolutionary martyrs ... but letting a comedian play a martyr, and promoting the film with ‘little fresh meat’ will do no good ... [and is] a foundation for historical nihilism.”

The phrase “little fresh meat” is a Chinese expression for handsome young actors. Ye said in a separate Weibo post that using “little fresh meat” to play central characters, including General Ye, was “distorting and insulting” revolutionary history.

Ye Ting is played by Oho Ou, 24, who first found fame on Hunan TV’s singing competition Super Boy in 2013.

The film’s producer, Huang Jianxin, also supported the decision to use young actors, as “youth is not something you can just play”.

The premiere was attended by the city’s leader, Carrie Lam Cheng Yuet-ngor, two of her predecessors – Leung Chun-ying and Tung Chee-hwa – the director of Beijing’s liaison office in the city, Zhang Xiaoming, and Yue Shixin, political commissar of the PLA Hong Kong garrison.

The film is the last in a trilogy, following The Founding of the Republic in 2009 and The Founding of the Party in 2011.